Funding Acknowledgements Type of funding sources: None. Introduction following cardiac resincronization therapy (CRT), QRS duration is the most important prognostic factor in the 12-lead electrocardiogram (ECG). However, there is little evidence regarding if the electrocardiographic pattern following CRT has impact on morbidity and mortality. Purpose In this historical cohort study we analysed if a certain pattern in three leads of the ECG (Rs in V1, Qr in aVL or rS in I) is associated with lower incidence of adverse outcomes in a population of CRT patients within 1 year of implant. Other variables previously associated with success or failure of CRT were analysed. Methods patients with CRT devices with left ventricle lead in the coronary sinus were included from January 2012 to April 2019. The primary endpoint was a composite of death of any cause and heart failure hospitalization at 1 year. Survival analysis was performed using Kaplan-Meier test, comparing survival graphics through Log-Rank test. For multivariate analysis, Cox regression was performed. Results 111 patients were included. Sample was divided into 2 groups according to the presence of the pattern in any of the three ECG leads. Baseline characteristics are reported in Table 1. Presence of any of the three patterns was independently associated with a lower incidence of the primary endpoint (2.3% vs. 17.6%, hazard ratio 0.1, 95% confidence interval 0.013-0.774, p = 0.016). Previous atrial fibrillation was also independently associated with a higher incidence of the primary endpoint. QRS duration postimplantation did not showed prognostic value. Conclusion the presence of the patterns Rs in V1, Qr in aVL or rS in I is an independent predictor of good prognosis in patients with CRT. Baseline characteristicsPattern Rs-V1/Qr-aVL/rS-INo patternp-valueAge (years)69 ± 1767 ± 210.257Women8 (18.6)17 (25)0.432Atrial fibrillation18 (41.9)22 (32.4)0.309- Ischemic cardiomyopathy- Non ischemic cardiomyopathy18 (41.9)25 (58.1)26 (38.8)41 (61.2)0.75Indication- HFrEF + NYHA II-IV + wide QRS- rEF + indication of cardiac stimulation- LV dysfunction secondary to stimulation 35 (81.4)7 (16.3)1 (2.3) 58 (85.3)9 (13.2)1 (1.5) 0.5870.6560.741Preimplantation LVEF (%)28 ± 1328 ± 150.882Up-titrated treatment17 (39.5)26 (38.2)0.891- LBBB- RBBB36 (83.7)5 (11.6)61 (89.7)6 (8.8)0.3550.63QRS duration postimplantation (ms)144 ± 35142 ± 500.657HFrEFheart failure with reduced ejection fraction; NYHA: New York Heart Association; rEF: reduced ejection fraction; LV: left ventricle; LVEF: left ventricle ejection fraction; LBBB: left bundle branch block; RBBB: right bundle branch block.Abstract Figure. Kaplan Meier survival curves

Introduction Following cardiac resincronization therapy (CRT), QRS duration is the most important prognostic factor in the 12-lead electrocardiogram (ECG). However, there is little evidence regarding if the electrocardiographic pattern following CRT has impact on morbidity and mortality. Purpose In this historical cohort study we analysed if a certain pattern in three leads of the ECG (Rs in V1, Qr in aVL or rS in I) is associated with lower incidence of adverse outcomes in a population of CRT patients within 1 year of implant. Other variables previously associated with success or failure of CRT were analysed. Methods Patients with CRT devices (pacemaker or defibrillator) with left ventricle lead in the coronary sinus were included from January 2012 to April 2019. One year clinical follow-up was performed. The primary endpoint was a composite of death of any cause and heart failure hospitalization. Differences in categorical data were reported as frequencies then compared using χ2 tests. Continuous variables were reported as means ± standard deviation with differences between groups tested using independent samples t-tests. Survival analysis was performed using Kaplan-Meier test, comparing survival graphics through Log-Rank test. For multivariate analysis, Cox regression was performed. Variables that showed significance in the univariate analysis were included. Results 111 patients were included. Sample was divided into 2 groups according to the presence of the pattern in any of the three ECG leads. Two patients (1.8%) presented Rs in V1 and Qr in aVL simultanously and two patients (1.8%) presented Rs in V1 and rS in I. None of the patients presented all three patterns simultaneously. Baseline characteristics are reported in Table 1. Presence of any of the three patterns was independently associated with a lower incidence of the primary endpoint (2.3% vs. 17.6%, hazard ratio 0.1, 95% confidence interval 0.013–0.774, p=0.016). Previous atrial fibrillation was also independently associated with a higher incidence of the primary endpoint. QRS duration postimplantation did not showed prognostic value. Conclusion The presence of the patterns Rs in V1, Qr in aVL or rS in I is an independent predictor of good prognosis in patients with CRT. Funding Acknowledgement Type of funding sources: None. Baseline characteristicsKaplan Meier survival curves